This invention relates to the levitation or positioning of an object by the use of remote forces such as acoustic, electromagnetic, or gas flow, which are imposed on the object in a non-contact fashion.
Various types of acoustic and other non-contact levitation techniques are well known. For example, acoustic levitation using tuned chambers are described in U.S. Pat. Nos. 3,882,732 and 4,054,181. Acoustic levitation in which a beam of sound is directed toward a small reflector is described in U.S. Pat. No. 4,284,403. Other known techniques include electromagnetic levitation and air jet or aerodynamic levitation, in which a stream of air is directed from beneath the object.
The above-identified application describes a method and apparatus for acoustic levitation in which an object is suspended between one or more pairs of opposed sound sources driven at the same frequency. The sound waves interfere to create a number of energy wells in which a specimen may be stably levitated or suspended. The phase of one sound source may be adjusted relative to the phase of the other source to move the position of the energy wells and cause the object to move.
A major proposed use of acoustic levitators is to process glass and ceramic materials in the microgravity of outer space. Electromagnetic levitation techniques are limited to the use of conductive specimens such as metals. With acoustic levitation, specimens of any type of material can be held in position while various experiments are being conducted. For example, a sample may be melted and cooled without any contact with a container, which eliminates any impurities being introduced by reason of contact of the sample with the container.
Acoustic levitation techniques on earth, however, are less effective because of the presence of gravity, especially if the levitated objects have a high density. The acoustical forces are relatively weak, and production of the necessary sound pressure levels is difficult. In addition, the production of high intensity sound results in distortions which are highly detrimental to levitation. The problems become intensified if the object is heated and cooled.
The use of a gas stream to levitate an object is advantageous because the lifting forces are considerably greater than those available with acoustic techniques. In the past, however, this technique has been limited to solid, spherical objects. The stream of gas causes the object to spin, which contributes to the lateral stability of a solid object, but typically prevents successful application to liquid objects. Generally, in the case of liquids or objects which are melted while being levitated the object flattens or otherwise changes shape and is ejected from the gas stream.